The present disclosure relates to a directional coupler that performs electromagnetic coupling for a plurality of high-frequency signals having different frequencies, relates to a high-frequency front-end module that includes the directional coupler, and relates to a communication device.
Japanese Unexamined Patent Application Publication No. 2004-40259 discloses a directional coupler that supports a plurality of high-frequency signals. The directional coupler disclosed in Japanese Unexamined Patent Application Publication No. 2004-40259 includes a first transmission line, a second transmission line, and a coupling line. The first transmission line transmits a high-frequency signal of a first frequency. The second transmission line transmits a high-frequency signal of a second frequency. The coupling line is coupled to the first transmission line and the second transmission line.
Regarded as an electrical circuit, each of the first transmission line and the second transmission line are coupled to the same part of the coupling line.
However, in the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2004-40259, the first transmission line and the second transmission line are arranged close to each other, and therefore the first transmission line and the second transmission line may become coupled with each other. Consequently, when the impedance of one of the transmission lines changes, the impedance of the other transmission line also changes and this is connected to degradation of the coupling performance.
In addition, in the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2004-40259, since each of the first transmission line and the second transmission line are coupled to the same part of the coupling line, it is not easy to optimize the coupling path length for the high-frequency signals transmitted through the respective transmission lines.